It is well known that vinyl resins may be plasticized or changed from the hard, horny and stiff state to a soft, plastic workable condition by the addition thereto at elevated temperatures of certain plasticizers, such as dioctyl phthalate, and the like. These vinyl polymers or resins are referred to as dispersion resins or paste resins and are usually made employing an emulsion polymerization technique, although a suspension polymerization process can be used.
When the vinyl resin is mixed or blended with a plasticizer, it is referred to as a "plastisol". By virtue of the flowability of the plastisol it can be processed into various useful products. The plastisols can be used in making molded products, coatings, and the like. Accordingly, the dispersion resin must be capable of being mixed with a plasticizer easily and uniformly to form low viscosity plastisols which are stable, containing particles of uniform and proper size, and capable of producing films, and like products, of good clarity.
With the customary emulsion polymerization processes, suitable latices have been difficult to obtain since the latices usually contain particles of varying size and are either too fine or too large. Various proposals have heretofore been made to overcome these difficulties but not with the ultimate success desired. For example, the use of various different emulsifiers and catalysts have been proposed. Also, varying the conditions of polymerization has been suggested. However, in most of these cases, too much coagulation occurred with the resulting latex containing too much coagulum or partially agglomerated particles which precipitate reducing the yield. Further, the shelf-life of such latices leave much to be desired. It is desirable to have latices which change very little during storage with respect to viscosity and have and maintain good heat stability.
Another frustrating and detrimental problem in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal CH.sub.2 .dbd.C&lt; group, is the formation of undesirable polymer build-up on the inner surfaces of the reactor. This deposit or build-up of polymer on said reactor surfaces not only interferes with heat transfer, but also decreases productivity and adversely affects polymer quality, such as producing finer particles than desired with the resultant adverse effect on viscosity. Obviously, this polymer build-up must be removed. If not, more build-up occurs rapidly on that already present resulting in a hard, insoluble crust.
In the past it was the practice to have an operator enter the reactor and scrape the polymer build-up off the walls and off the baffles and agitators. This operation was not only costly, both in labor and down-time of the reactor, but presented potential health hazards as well. Various methods have heretofore been proposed to remove the polymer build-up, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like, but none has proved to be the ultimate in polymer build-up removal. It would be desirable, of course, to have a polymerization process in which polymer build-up does not occur. Unfortunately, none of the known emulsion polymerization processes are capable of solving this, and the other problems reiterated above. There is a definite need in the art for a polymerization process which meets all these criteria.